1. Field of the Invention
The invention relates to the field of cargo carrying vehicles such as trailers for tractor/trailer combinations. In particular, a heavy duty trailer for short haul transport of intermodal containers is provided to facilitate loading and unloading. The trailer of the invention is configured to accept containers of different sizes as well as plural containers such as two half-length containers, using centrally located retractable positioning devices. The trailer enables accurate relative positioning of two half-length intermodal containers on a trailer that accommodates various container sizes and thus lacks fixed flanges against which the containers might be abutted for positioning. Raisable side wings are deployable to engage the corners of the containers, and position them sufficiently accurately that two half length trailers can be handled as a unit.
2. Prior Art
Intermodal containers provide an efficient shipping means in that they can be carried by ship, by rail, by truck, etc. Intermodal containers have standard lower corner fittings enabling them to be attached to complementary fittings on trailers, rail cars and the like, as well as upper corner fittings that can be engaged by stacking loaders, cranes and the like. Internationally standard container lengths are nominally 20 and 40 feet (about 6.1 and 12.2 meters). However, nominal 20 foot containers are actually made shorter than 20 feet such that two 20 foot containers with a slight clearance between them can be handled by some of the same equipment as for a 40 foot container (i.e., when positioned at the exact clearance needed to place the outer engagement fittings of the two containers at the positions occupied by those of a 40 foot container). More particularly, a nominal 20 foot container is actually 238.5 inches in length. Correct positioning requires that the two short containers by placed with an exact three inch clearance so that the combined length (including clearance) is 40 feet.
The containers can be engaged at their corner fittings, for example, with twist-lock mechanisms that are positioned to complement the container size. Although there is a margin for error and "floating" twist locks are known, even floating twist locks are only capable of about an inch of lateral displacement. Therefore, positioning is a problem.
All containers come in the same width. Containers are also used, primarily in the USA, in lengths of 45, 48 and 53 feet (about 14, 15 and 16 meters, respectively). The mountings on the trailers, rail cars or the like for carrying the containers have their corner-engaging fittings spaced appropriately for the particular size of trailer. For railroad carriage, a flatbed car may have relocatable corner engaging fittings. For typical a tractor/trailer carriage, the trailer chassis is specific to the particular container length and can carry only one type of container. A trailer capable of handling all such containers must have a bed area as large as the largest container. This aggravates the problem with accurately positioning smaller containers and double half-length containers because it is not readily possible to provide highly efficient locating devices (especially corner engagement couplings) for small containers without occupying the space needed for larger containers.
It would improve efficiency in the handling of containers, especially pairs of half length containers such as so-called "double twenty picks," if the containers could be initially placed with high accuracy. Once correct positioning is obtained, subsequent handling of the containers at least partly using engagement mechanisms for full length containers, does not disturb the correct positioning.
For over-the-road travel, a container is placed on the trailer of a tractor/trailer rig and all four corners of the container are engaged by lockable fittings that secure the container to the trailer. For example, an engagement pin in the trailer can be raised into an opening in the box-like corner structure and twisted to lock the container to the trailer chassis. Containers also can be attached to one another by inter-box connectors having protruding pins, in which event the inter-box connectors can engage in openings in the trailer, rail car or the like. For example, two nominally 20 foot containers can be coupled to one another end to end, and handled using stacking loaders, cranes, trailers and/or rail car repositories that otherwise would handle one 40 foot container.
When loading and unloading a number of containers, for example when unloading containers from a ship or otherwise changing transportation modes for a number of containers, it is important to proceed as quickly as possible. When a ship is being loaded or unloaded in port, the ship is not serving its primary function of transporting cargo, and is not generating income. However, time spent in loading and unloading is unavoidable. To minimize the time spent, for example when unloading containers from a ship, all the containers that need to be unloaded from the ship are unloaded at once to a holding area, using a fleet of transfer trailers that repetitively carry containers from an off-loading area near the ship to an intermediate area of the yard or the like. The ship is thus unloaded quickly. The individual containers are processed later, through more time-consuming steps such as identifying the containers and their destinations, affixing the containers to trailers of appropriate length, and dispatching them to their destinations. Similar steps can be undertaken for loading containers onto a ship, namely preliminary storing the containers destined for a particular ship in a holding area from which the containers can be transferred by repetitive trips using transfer tailers, for loading onto the ship as quickly as the shipyard crane can be operated.
Container ships are generally unloaded by cranes having grappling devices engageable with corners of containers, spaced to couple to single containers or to two or more containers that may be attached but at least must be positioned correctly. For example, a crane may have a boom with a carriage that can be moved over the ship. The grapples are lowered from the carriage to engage a container. The container is lifted over the gunwale and lowered onto the next transport tractor/trailer in a line waiting alongside. However, the crane may be the most expensive and slowest element of the container handling apparatus. It would be advantageous if the crane could proceed unimpeded by the need to correct for imprecise positioning of the containers.
Due to the urge to proceed quickly, a container often is set down rather hard on the transfer trailer. The transfer trailer and its container are removed immediately to clear the way for the next transfer trailer and container. At the intermediate storage point, the container is removed from the trailer by a crane or stacking loader, and the trailer is brought immediately back for another cycle.
It is not necessary during preliminary movement or transfer of containers between an intermediate storage area and a loading or unloading station, to undertake all the same securing steps for affixing the container to the trailer as would be appropriate for over-the-road travel. However, couplings are useful for correctly positioning containers on the trailers for transfer, especially when two or more containers are to be transferred end-to-end.
A problem is presented when the containers to be processed are not all the same size. Even if the containers are of a standard size, it is advantageous also to have the capability of handling a plurality of fractional size containers as a unit, such as two twenty-foot containers on a trailer that is dimensioned for one forty-foot container. It is possible to envision a trailer having alternative fittings spaced to accommodate all the container sizes and combination options that might be encountered, but fittings for smaller (shorter) containers and for plural combined containers could interfere with larger containers. It is also possible to envision corner fittings that are moveable to accommodate different sizes; however, this solution also carries the possibility of damage or interference if one attempts during the hurried unloading of a ship to place a container on fittings that are not properly positioned. These solutions are cumbersome. What is needed is a trailer in which one trailer size fits all containers, provision is made for carrying multiple containers and/or attached containers, and containers can be quickly and dependably positioned for transport.